This invention relates to the precision coating of surfaces and more particularly to extrusion coating of substrates wherein fluid storage, delivery, and dispensing means are contained within a module which can be removably attached to a station containing the remainder of a complete coating apparatus.
It is often necessary or desired to provide a coating of a particular substrate. For example, in the video electronics industry it is often desired to coat panels which will serve as flat panel displays (FPD) to be incorporated into television sets, computer monitors and the like. It is important in such applications to ensure the accuracy and consistency of coating thicknesses across the panel.
In the prior art, the fluid delivery means, including fluid supply, pumps, and dispenser or fluid extrusion head assembly, as well as the chuck, substrate and means for distributing a coating of the fluid on the substrate were all part of a single integrated coating apparatus assembly. As such, when it was necessary to change coating fluids, or perform other operations on the fluid delivery means, the entire coating apparatus would be idled. Fluid changeover operations include time consuming tasks such as cleaning all tubing, pumping mechanisms, and essentially all surfaces where residue of the previous coating material could be present. This thoroughness is often necessary because of potentially dangerous chemical reactions between two different coating materials to be used in succession, and because of the danger of cross-contamination between coating materials used in different processes. The idle time for the coating apparatus is expensive and wasteful given that mechanisms unrelated to the fluid delivery system are idled by the operations necessary for fluid changeover. Accordingly, a need exists in the art for a system and method wherein a chuck assembly adapted to position and hold substrates to be coated as well as other components and materials used in the coating process but not part of the fluid delivery system are not left idle during fluid delivery system cleaning operations.
Additionally, in order to avoid dripping or smearing coating material which has gathered around the extrusion head after a coating operation, it is often necessary to clean the extrusion head before a new coating operation begins. In the prior art, cleaning of extrusion mechanisms is usually accomplished manually, potentially leading to inconsistent results and disruption and delay of the coating operations. Therefore, it is a problem in the art that manual cleaning operations are inconsistent and unreliable.
In order to ensure that coating material is applied consistently and evenly right from the start of the coating operation, it is desirable to ensure that a bead is fully and properly formed at the extrusion head prior to starting the coating process. A problem in the prior art exists with respect to properly priming fluid extrusion heads so as to ensure that a proper bead is formed prior to extruding fluid over the substrate, that a consistent rate of coating fluid flow is thereafter achieved, and that the extrusion head can be quickly moved from the priming mechanism to the substrate.
Generally, in prior art coating systems, there is a single pump mechanism located remotely from the extrusion head with appropriate fluid conducting means leading from the pump the head. The use of a single pump, while perhaps economical, makes it difficult to precisely control fluid flow at the extrusion head. Specifically, it may be difficult to start and stop at precisely defined moments and to establish the precise fluid flow rate desired.
In prior art systems, variation in the height of the extrusion head with respect to the substrate can cause breaking of the coating bead and variation in coating thickness. The causes of such height variation include part dimension variation, part placement error, and gradual drift in machine dimensions over time. Accordingly, there is a need in the art for a system and method for ensuring constant extrusion head height over the substrate being coated.
Accordingly, there is a need in the art for a method and system for coating in which the idle time for apparatus not part of the fluid delivery process to be minimized while fluid is being changed or recharged.
A still further need in the art exists for a cleaning station whose functions are automatically accessible to a fluid dispenser in between coating operations.
A still further need in the art exists for a priming station which can be accessed automatically by a fluid dispenser in between coating operations.
A still further need in the art exists for more precisely controllable flow of coating material at the extrusion head.
These and other objects, features and technical advantages are achieved by a system and method in which the wet components, including the fluid supply, pumping means, fluid dispensing head and utility station operations are located on a carrier, or other device, hereinafter referred to as a mobile device or cart, although it should be appreciated that the present invention may be embodied in any number of devices not completely consistent with the chosen nomenclature, which is removably attachable to the remainder of the coating apparatus. The mobile device is preferably in the form of a cart or fluid station which contains all or substantially all of the components in the coating apparatus which come into contact with coating fluid. The portion of the coating apparatus not part of this mobile fluid module, or fluid cart would preferably contain a chuck and shuttle mechanism, or other transport means. The non-fluid portion of the coating apparatus will be referred to as a base station or work station.
The fluid cart and base station preferably both contain means for being secured together in preparation for a coating operation employing a chosen cart. Means for accomplishing this attachment include but are not limited to clips, clamps, rollers on beams which are forced against a rigid surface, and grippers which may be actuated by electrical, pneumatic, and hydraulic means. Preferably, in the context of a plurality of carts with different coating materials and different types of dispensers on board, and possibly, a plurality of base stations, any cart can be mechanically attached, and appropriately interfaced to any station among the plurality of carts and stations, wherein the interface may serve to transfer information, power, and facility connections such as exhaust or drain connections, by a variety of means including electric, pneumatic, hydraulic, or wireless.
Preferably, both the fluid cart and base station both comprise means for communicating with the other. The need for coordinating fluid flow rates with relative velocity of the dispenser with respect to a substrate among other parameters create a desire for such communication. The communication link between the cart and base station may be made by wire or cable or may be wireless, and is preferably under computer control. If the communication is accomplished via a hard wire connection, this connection will preferably be automatically made when the cart and base station are mechanically joined. Alternatively, the wired connection may be made manually either before or after a rigid mechanical attachment between the cart and base station is accomplished. Upon removing a cart from a base station, all connections made when first joining the cart and base station are disconnected.
In a preferred embodiment, the dispenser, coating head, or extrusion head is associated with a cart as is other equipment with comes into direct contact with the coating fluid. This approach obviates the need to clean the dispenser in between coating operations involving different fluids, and minimizes the amount of mechanical connection and disconnection necessary when changing carts. A preferred embodiment of the cart includes a cowl assembly substantially sealing any exposed wet components, such as the aforementioned head, in order to allow their continued contact with the coating fluid without fear of contamination or evaporation when not in use. Accordingly, various carts may be configured for particular coating operations which are repeated throughout a day or week without requiring the cart to be fully checked when idle, but expected to be subsequently put back into service.
In order to properly service fluid carts when they are not attached to base stations and engaged in coating activity, docking stations are deployed which provide connections for operating equipment on the cart, such connections including but not limited to electrical, pneumatic, hydraulic, and wireless. In a preferred embodiment, servicing the carts requires that the various pumps, switches, and other devices be powered and properly controlled. The docking station also provides appropriate connections and control as well as appropriate containers and supplies for removing unwanted fluid from the cart, supplying fresh fluid to the cart, and for appropriately cleaning equipment on the cart.
Preferably, fluid supplied to the cart from the docking station includes fresh coating material, and fresh solvent of one or more types used in the head cleaning and priming operations on the fluid cart. Fluid removed from the cart to the docking station includes coating material which is not needed in a subsequent operation, or which has degraded over time to an unacceptable level of quality, or otherwise become contaminated, and used solvent material from the cleaning and priming assembly. The used solvent from the cleaning and priming operations may optionally be subsequently transferred to recycle and recovery station.
The following discussion acknowledges various possible relative motion configurations which may be used by a coating apparatus adapted according to the present invention. For example, a primarily moving head configuration is one in which the majority of the relative motion of a substrate with respect to a dispenser or dispensing head is due to movement of the dispenser over a mostly stationary substrate. Conversely, a primarily moving substrate, or moving chuck configuration is one in which the majority of the coating motion is due to motion of the chuck and substrate (it is assumed here that the substrate does not move with respect to the chuck) under a mostly stationary head, such as by the substrate being moved with respect to the dispenser during deposit of the fluid or by allowing a pool of fluid to be deposited and then spinning the chuck and substrate to distribute the fluid. Motion of the dispenser with respect to substrate could be initiated by means on either the cart or the base station, or both.
In a preferred embodiment of the invention, the base station is able to perform the same fluid removal and replenishment operations with respect to the fluid cart as described above in connection with the docking station.
Preferably, upon attachment of a preferred embodiment cart to a base station, a preferred embodiment dispenser would then be appropriately mechanically attached to a mount on the base station, whether a primarily moving head or primarily moving substrate configuration is in place. In the case of the moving head configuration, the mount for the dispenser would be attached to a shuttle mechanism or transport system which would move the dispenser over the substrate. In the case of a moving substrate configuration, the dispenser would be mounted on a point accurately fixed with respect to the chuck and substrate moving underneath the mounting point. Of course, the cart may include a shuttle or gantry assembly allowing the dispenser to be mounted thereon and positioned properly with respect to the base station without actually mounting the dispenser to the base station, if desired.
Even after being mechanically positioned on the base station, the dispenser would remain in communication with the cart, as the cart would continue to supply fluid to the dispenser, and in a preferred embodiment, to supply power and control information to a pump integrally mounted on the dispenser. Therefore, the cart will at least have a fluid connection to the dispenser. Additional possible connections between the dispenser and fluid cart include but are not limited to electrical control cabling, wireless broadcast, pneumatic lines, hydraulic lines (other than for coating fluid).
Mechanically mounting the dispenser on a portion of the base station permits the benefits the positioning accuracy of various parts of the base station with respect to each other to govern the relative locating accuracy between the dispenser and the substrate surface, and diminishes the level of precision required in the positioning of the cart with respect to the base station. The cart should nevertheless preferably be rigidly enough attached to the station so that no disruption in the various fluid and other connections occurs. However, mechanically mounting the dispenser on the base station means that imperfect mating of a cart and a base station when they are first attached, or minor relative movement of two with respect to each other during coating should not affect the mechanical precision of the coating operation. Moving the dispenser from the cart to the base station mount can be accomplished either manually, or automatically, preferably under computer control.
As mentioned above, the inventive mechanism is not restricted to an embodiment in which the dispenser is mounted to a portion of the base station in preparation for the coating operation. In an alternative embodiment, the dispenser could remain on or mountably attached to the fluid cart during coating. This embodiment may place an increased burden on the accuracy of positioning of the cart or at least the mechanism used to mount the dispenser with respect to the base station while the two are attached where relative positions of the dispenser and substrate are critical.
Using the present invention, each cart may be associated with a particular fluid or with a particular size or type of coating head. When a cart becomes unusable such as because the fluid supply has been exhausted, the fluid supply becomes unusable due to degradation over time, or because the current manufacturing process requires using a different coating fluid, the attached cart can be readily and rapidly disconnected from the base station. A new cart can then be immediately attached to the main station, and the dispensing head on the new cart attached to an appropriate mounting position on the base station.
Coating operations can thus quickly resume independently of the time consuming task of cleaning and readying for operation the fluid system on the old cart. The old cart can be cleaned and prepared for renewed operation at a docking station in parallel with the resumption of coating operations at the very same base station. The idle time experienced in the systems of the prior art is thereby minimized since coating operations need cease only during the disconnection and connection of carts and relocation of dispensing heads.
In a preferred embodiment of the present invention, utilities for servicing the fluid dispensing head may be located on each fluid cart within a range of travel of the fluid dispensing head as carried by a shuttle mechanism or other transport system of the preferred embodiment base station. Locating such utilities on the cart permits the features of the utilities, including but not limited to cleaning and priming of the dispenser, to be optimized for the fluid and dispensing head resident on that cart. For example, a cart carrying a particular fluid and a particular dispenser would contain scrubbers and solvents particularly suited for both the fluid and dispenser associated with that cart. Otherwise stated, the various components present on, or associated with a particular cart can be coordinated with each other for optimum system performance.
A shuttle on the base station can be automatically programmed to stop at utility stations on the fluid cart at appropriately selected times, such as between coating operations. A set of utilities could include a scrubbing station at which bulk coating material would be removed from the dispensing head through a combination of physical scrubbing with brushes in combination with use of a solvent. Such a scrubbing station is particularly useful if the most recently used coating material is highly viscous.
Another operation among these utilities preferably consists of a rinsing station at which a powerful solvent removes any material remaining from the most recent coating operation, even if the dispensing has been cleaned at the scrubbing station. The solvent used at the rinsing station is preferably selected so as to remove any solvent remaining from the scrubbing operation and any residual coating material, and so as to evaporate rapidly after completion of the rinsing operation thereby obviating the need for any further cleaning action.
Yet another operation among these utilities could consist of a priming station at which the dispensing head could be placed so as to ensure that a full and consistent bead of coating fluid is made ready at the dispensing head in preparation for the next coating operation, as well as to extract any coating fluid from the dispenser which may have been contaminated with or diluted by a cleaning solvent or other matter. A preferred embodiment for such a priming station consists of rotating cylinder upon which coating fluid is placed in the smallest quantity necessary to establish a consistent bead or to remove contaminated coating fluid from the dispenser. In this embodiment, holding the dispensing head stationary in proximity to the rotating cylinder effectively simulates moving the dispensing head over a certain length of surface material, without requiring the space such a length of surface material would occupy.
In a preferred embodiment of the present invention, at least one primary pump located remotely from the dispensing head, preferably on the fluid cart, would pressurize the fluid connections leading up to a dispensing head assembly, and a second smaller pump, preferably integrated into the dispensing head assembly, would accurately control the flow of fluid to be dispensed or extruded onto the substrate surface. Implementation of such an integrated pump on head arrangement would require communication and control connections to be made between the cart and the dispensing head. These connections, as well as the main coating material fluid connection are preferably coiled and located in such a manner as to not have their function disrupted in any way by motion of the dispenser on a shuttle mechanism or other transport means. A preferred mechanism for avoiding interference with the various cables, tubes, hoses and the like, necessary for connections to the dispenser and shuttle mechanisms and other devices, is the deployment of troughs preferably along the sides of the base station in which these connecting means may be placed.
In a preferred embodiment of the present invention, the means for moving the head and substrate to be coated with respect to each other is achieved by moving the head over a mostly stationary substrate. Using this embodiment, the footprint of the apparatus in the horizontal plane is much reduced with respect to a configuration in which the substrate travels a distance equal to its own length underneath a fluid dispenser. Using the moving head embodiment, the length of the system need only exceed the length of the substrate by the amount necessary for the fluid dispensing mechanism to move clear of the substrate, for purposes of substrate placement and removal, and possibly for the placement of utilities to service the fluid dispenser in between coating operations.
The moving head embodiment is adaptable to large substrate sizes as the nature of the chuck assembly design would change little with increasing substrate size. A single coating apparatus can be used with substrates of different sizes by employing a head of appropriate length and ensuring the shuttle mechanism has sufficient travel to cover the lengths of the various substrates to be coated. Where a larger substrate cannot be accommodated by a particular coating apparatus, the principal changes required for such apparatus to accommodate a larger substrate would be to appropriately increase either the width and/or travel of the shuttle mechanism and the length (span) of the fluid dispenser, and to adjust the size the chuck. Increasing the size of the substrate does not significantly increase the stresses on the moving means in a moving head embodiment. Whereas, in a moving substrate environment, the weight to be carried by the moving means, and the stresses thereon increase considerably with increasing substrate size.
A shuttle mechanism which carries the fluid dispenser preferably rides on an air bearing or alternative support and guidance mechanisms such as rolling contact with a rail system, or low friction contact surface, located underneath the chuck assembly, the shuttle mechanism thereby forming a single continuous rigid loop structure. The rigidity of this design optimizes the precision with which the coating apparatus can operate. This configuration also limits the width of the apparatus by obviating the need for a support surface beyond the width of the chuck assembly, thereby further reducing the footprint of the coating apparatus. The shuttle mechanism, with its air bearing below the chuck a carriage to carry the fluid dispenser above the chuck and substrate, and structural links connecting the two, effectively envelops the chuck thereby restricting the permitted thickness of the chuck assembly and equipment contained therein.
Although the modular fluid cart concept is preferably employed in conjunction with coating apparatus employing a moving head apparatus, the concept is not limited to this configuration. The modular fluid cart could be attached to a base station wherein the substrate to be coated moves underneath a mostly stationary dispensing head, or extrusion head. More generally, the base station to which the fluid cart is attached could employ any combination of dispenser and substrate movement in order to accomplish an appropriate coating motion.
Accordingly, it is a technical advantage of the present invention that the idle time for apparatus not part of the fluid delivery process is minimized while coating fluid is changed or recharged.
It is a further advantage of a preferred embodiment of the present invention that the various devices and utilities located on a particular fluid cart may be selected for optimal interaction with each other.
It is a still further advantage of the present invention that flow of coating material at the dispensing head is more precisely controllable than in prior art systems.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.